1. Field of the Invention
The invention relates to crosslinked polyether polyol sealants which contain urethane crosslinks and provide electrical connections under normal operating conditions and at elevated temperatures, and to insulation displacement connectors containing such sealants.
2. Description of the Art
Polyol-containing sealants are known in the art.
U.S. Pat. No. 5,064,494, (Duck et al.) discloses a sealant composition made from a polyol based isocyanate prepolymer and a heat activatable blocked complexed amine. The materials are cured by briefly heating to above 120.degree. C. and subsequently moisture cured.
U.S. Pat. No. 5,061,749 (Ito et al.) discloses a polyol based isocyanate prepolymer and a vinyl polymer containing a hydrolyzable siloxy group. The material is stated to be useful as a sealing material when formulated with proper fillers and plasticizers.
U.S. Pat. No. 5,053,465 (Waddill) discloses sealers comprising a polyol based blocked isocyanate prepolymer epoxy resin blend cured with a polyether polyamine.
U.S. Pat. No. 5,034,435 (Squiller) discloses aqueously dispersed polyol based blocked isocyanate-terminated prepolymer epoxy compositions which are mixed with aliphatic polyamines to form a sealant.
U.S. Pat. No. 5,151,484 (Schmalsteig et al.) discloses isocyanate prepolymers containing ether and ester groups which are used as binders in low solvent or solvent-free, low viscosity, polyurethane coating compositions, sealing compositions or casting compositions.
Sealants are also known for use in insulation displacement connectors. U.S. Pat. No. 4,645,285 discloses an electrical terminal having a slotted insulation displacement section, wherein the terminal is protected by a two-part enclosure. The enclosure is filled with a closed foam sealant. Various foam compositions are disclosed including polyether urethanes, and polyester urethanes having Shore A stiffness values of from about 50 to about 70. The composition is disclosed to be useful up to 250.degree. C., and 97% humidity.
U.S. Pat. No. 4,746,381 discloses an end cap connection which provides a strong mechanical bond and a fluid resistant seal wherein the cap contains a quantity of synthetic resin adhesive. The synthetic resin is disclosed to be a blend of epoxy resins, rubber modifiers, and flexibilizers. No urethane crosslinked compositions are disclosed.
U.S. Pat. No. 4,680,233 discloses a two-layer sealing material which comprises a layer of elastomeric sealant having a cone penetration of from about 100 (10.sup.-1 mm) to about 350 (10.sup.-1 mm) and an ultimate elongation of at least 50% and a surface layer of air drying material to permit placement and handling of the sealant and reduce the surface tack of the sealant. It is disclosed that the elastomeric sealants generally have an uncrosslinked oil compound which renders the surface oily. Sealants are disclosed as useful include polysiloxanes, polyurethanes, polybutyls, triblock copolymers and the like.
U.S. Pat. No. 5,069,637 discloses an electrical connector including a contact assembly placed in a cavity. The cavity is sealed except for conductor inlets, and contains a water-proofing or sealing compound. Silicone grease is the only specific sealant disclosed.
U.S. Pat. No. 5,080,606 discloses an electrical connector for interconnecting a variable number of wires in a stacked, in-line configuration. The connector includes a body for receiving the wires, a metallic contact element located within the body and a cover; the body has front and rear walls each having three holes in a stacked, nonlinear arrangement. The connector contains a sealant. Silicone grease is the only sealant specifically disclosed.
U.S. Pat. No. 5,090,917 discloses an electrical connector containing an insulation displacing contact inside a housing. The housing contains a sealing material around the contact which is identified only as a "gel".
The final three references describe insulation displacement connectors which are housed in a sealant containing enclosure. When it is desired to make an electrical connection with sealant already in place, it has been difficult to find a sealant which satisfies the rigorous demands of electrical insulation and environmental protection.
Three critical requirements must be met. Firstly, the sealant must be soft enough so that it will yield to the insertion of thin cross-section wires prior to insulation displacement connection. Secondly, the sealant must possess enough flow to conform to the contours of the inserted wires. Finally, it must also prevent moisture and other environmental contaminants from reaching the connection. These environmental contaminants include such compositions as insecticides, detergents and the like.
These sealants are typically formulated using one of three approaches; gels formed from liquids by adding particulate fillers to raise viscosity, gels formed from solid materials softened by plasticizers, and greases.
While various of these gel sealants will adequately provide both the required environmental sealing and electrical insulation at room temperature, gel sealants tend to lose their viscosity as the ambient temperature increases, and may begin to exhibit fluid flow characteristics. The sealant may even flow away from the IDC enclosure, leaving the electrical connection unprotected. Further, the sealant will be susceptible to attack by moisture, and other environmental stresses, further reducing its protective properties.
Effective sealant materials for IDCs may also be formed from polyurethane compositions. However, these materials are generally too rigid when cured to conform to the contours required. This is especially true when the polyurethane composition contains a stoichiometric excess of isocyanate component. The typical solution for this rigidity is to plasticize the composition; however, highly plasticized polyurethane compositions are extremely susceptible to degradation by fluid contaminants, such as detergent solutions and hydrocarbon fluids.
The present inventor has now discovered that certain polyether polyols or polyether polyamines lightly crosslinked using a stoichiometric deficit of an isocyanate reactant provide sealant compositions which overcome the deficiencies of prior art sealants used in IDC enclosures and void spaces incompletely enclosed. In the instant case, the reaction between polyether species and isocyanate species results in a gel-like polymer which is lightly crosslinked through urethane linkages. The resulting polymer material exhibits all the desirable electrical properties and environmental protection and is a soft, conformable sealant without containing any plasticizers which could increase susceptibility to environmental contaminants. In fact, no fillers or adjuvants are required to provide sealant compositions having the desirable electrical properties and conformability.